This invention relates generally to vehicle lifts and their controls, and more particularly to a vehicle lift control adapted for maintaining multiple points of a lift system within the same horizontal plane during vertical movement of the lift superstructure by synchronizing the movement thereof. The invention is disclosed in conjunction with a hydraulic fluid control system, although equally applicable to an electrically actuated system.
There are a variety of vehicle lift types which have more than one independent vertically movable superstructure. Examples of such lifts are those commonly referred to as two post and four post lifts. Other examples of such lifts include parallelogram lifts, scissors lifts and portable lifts. The movement of the superstructure may be linear or non-linear, and may have a horizontal motion component in addition to the vertical movement component. As defined by the Automotive Lift Institute ALI ALCTV-1998 standards, the types of vehicle lift superstructures include frame engaging type, axle engaging type, roll on/drive on type and fork type. As used herein, superstructure includes all vehicle lifting interfaces between the lifting apparatus and the vehicle, of any configuration now known or later developed.
Such lifts include respective actuators for each independently moveable superstructure to effect the vertical movement. Although typically the actuators are hydraulic, electromechanical actuators, such as a screw type, are also used.
Various factors affect the vertical movement of superstructures, such as unequal loading, wear, and inherent differences in the actuators, such as hydraulic components for hydraulically actuated lifts. Differences in the respective vertical positions of the independently superstructures can pose significant problems. Synchronizing the vertical movement of each superstructure in order to maintain them in the same horizontal plane requires precisely controlling each respective actuator relative to the others to match the vertical movements, despite the differences which exist between each respective actuator.